Method of making electroluminescent phosphors with small particle sizes and powder with D50 value of no more than 10 micrometers
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United States of America Patent
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Oct 30, 2007
Grant Date -
Oct 5, 2006
app pub date -
Mar 30, 2005
filing date -
Mar 30, 2005
priority date (Note) -
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Abstract
An electroluminescent phosphor powder includes copper-activated zinc sulfide particles that have a size distribution with a D50 value of no more than 10 .mu.m, where no more than 25% of the particles have a size greater than about 15 .mu.m and/or a 24-hr brightness of at least 15 footlamberts. These particles are made by a method that includes first firing copper-doped zinc sulfide mixed with zinc oxide, sulfur and a chloride-containing flux, rapidly cooling the mixture to below 100.degree. C., and then mulling and second firing the mixture to provide a powder. The powder can then be elutriated to provide the electroluminescent powder with a narrow particle size distribution (more than 90% between about 5 and 15 .mu.m). The elutriating step can be avoided (albeit with a slightly wider size distribution) by more tightly controlling the first firing temperature.
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